What do the flags g, i, m, and s mean?

g (global) finds all matches instead of just the first; i (ignore case) matches upper and lowercase; m (multiline) makes ^ and $ match line boundaries; s (dot-all) lets . match newlines.

Why does my regex show an error?

The pattern is invalid JavaScript regex syntax, for example an unclosed bracket or parenthesis, or an unknown escape. The tool shows the engine's exact error message to help you fix it.

Is my test data sent anywhere?

No. All matching happens locally in your browser with the built-in regex engine. Your pattern and test text never leave your device.

Regex Tester

Test regular expressions live with highlighted matches

Regular expression

gglobalicase-insensitivemmultilinesdot matches newlines

Test string

Matches will appear here…

0 matches found

Uses your browser's built-in JavaScript regex engine. Nothing is sent or stored anywhere.

About this tool

A regex tester is the fastest way to build confidence in a regular expression before it ships in your code. Writing patterns for emails, phone numbers, log parsing, or input validation by trial and error in a console is slow; JoliTools' free regex tester gives you instant visual feedback. Every match in your test string is highlighted in yellow, with a live count and a breakdown of each capture group, so you can see exactly what your pattern catches, and what it misses.

Getting flags right matters as much as the pattern itself. This tester includes one-click toggles for the four most common JavaScript flags: global (g), case-insensitive (i), multiline (m), and dot-all (s). It also validates your syntax in real time and shows the regex engine's exact error message when a pattern is invalid, which turns cryptic debugging into a quick fix.

How to use the regex tester

1Type your regular expression into the pattern field (JavaScript syntax).
2Toggle the flags you need: g (global), i (case-insensitive), m (multiline), s (dot-all).
3Paste or type your test string into the textarea.
4Matches are highlighted instantly, with a count and per-match capture group details.
5Click “Load sample” to try an email-matching example, or “Clear” to start over.

Good to know

Because everything runs locally in your browser using the built-in JavaScript RegExp engine, there is nothing to install and no account to create. The syntax you test here behaves identically to RegExp in your frontend or Node.js code. Your patterns and test data stay on your device, ideal when you are testing against real logs or sample data you cannot upload anywhere.